Safari not opening Yahoo, Google, or You Tube home pages.

Hello,

I do not have any antivirus or parental control software installed...

Thank you Linc Davis (and Kamper72). Tried all other remedies suggested by everyone in this group concerning extensions, plug-ins etc,. all to naught. Spent months on and off dealing with having to "reload page" and double, triple click on the back button to get a previous page. Then, with help from you and "Kamper72," I hit the jackpot. I had the same problem as 72, not being able to connect at all when IPv6 disabled on the Safari network settings. But, thanks to 72, I also had Avast installed, and when I disabled the IPv6 in Avast's settings for both web and email data, everything has been working fine since. I was just about to abandon Safari as a piece of you-know-what until now. And still, I question exactly why Safari won't work when Firefox seems to work fine with the same settings. In any event, if running Avast, or any other anti-virus or firewall, check these firewall settings before going through all the other Safari preferences and settings. You might save yourself a lot of time. Like Linc says, the old PC adapted firewalls are a source of nothing but problems.

This fixed it:

"Select  ▹ System Preferences ▹ Network ▹ Advanced ▹ Proxies. If any proxies are selected, deselect them, apply your changes, and try again. You must apply the changes before they take effect. You don’t need to change the other settings".

The issue arose spontaneously while browsing with Safari. It has happened several times in the last year with different Safari versions including 10.0 (11602.1.43). The error message from Safari is wrong:

"Safari can’t open the page... because the server unexpectedly dropped the connection. This sometimes occurs when the server is busy. Wait for a few minutes, and then try again".

Yet, Google Chrome has the same issue, but generates a true informative error and how to fix it, pointing to proxies in Details section, as Linc Davis points out. It would be much useful if Safari error messages were also truly informative and not general useless ones as that one above.